This application is based on Japanese Patent Application No. 2000-041659 filed Feb. 18, 2000, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates in general to a method of producing a hollow piston for a compressor of reciprocating type.
2. Discussion of the Related Art
In general, a piston for a reciprocating type compressor has a head portion which is slidably fitted in a cylinder bore of the compressor, and an engaging portion which engages a reciprocating drive device of the compressor for reciprocating the piston. Upon actuation of the reciprocating drive device with the engaging portion of the piston being in engagement with the reciprocating drive device, the piston is moved such that the head portion of the piston is reciprocated in the cylinder bore to effect suction and compression of a gas. A swash plate type compressor is one example of the compressor which uses such a piston. In the piston used for the swash plate type compressor, the engaging portion is generally U-shaped, and engages the opposite surfaces of the swash plate of the compressor through a pair of shoes. The piston is reciprocated by a rotary movement of the swash plate.
For reducing the weight of the piston for the compressor, at least the head portion of the piston is made hollow. As disclosed in JP-A-11-303747 and JP-A-11-294320, such a piston is produced by preparing a hollow cylindrical member having an open end at at least one of its opposite ends, and a closure member, and closing the open end of the hollow cylindrical member with the closure member. According to the methods disclosed in those publications, a hollow head portion of the piston is formed by closing, with the closure member, an open end of a body member of a blank for manufacturing the piston, which body member of the blank includes a bottom portion and a hollow cylindrical portion. When the body member of the blank is formed integrally with the engaging portion, the closure member is a circular plate member, or a cylindrical member including a circular bottom plate portion and a cylindrical portion. When the body member of the blank is separate from the engaging portion, the closure member is formed integrally with the engaging portion.
Where the head portion of the piston is formed by closing the open end of the hollow cylindrical member with the closure member, it is generally known that one of the hollow cylindrical member and the closure member is formed to have a female corner portion which is defined by an annular shoulder surface and a circumferential surface adjacent to the shoulder surface, while the other of the hollow cylindrical member and the closure member is formed to have a male corner portion which corresponds to the female corner portion. If the closure member includes an annular abutting surface which is to be held in abutting contact with an end face of the hollow cylindrical member at its open end, and a radially inner fitting portion which protrudes axially from the annular abutting surface and which is to be inserted into the open end of the hollow cylindrical member, for instance, the annular abutting surface of the closure member functioning as the shoulder surface cooperates with an outer circumferential surface of the fitting portion to define the female corner portion, while the open end portion of the hollow cylindrical member defines the male corner portion. If the open end portion of the hollow cylindrical member includes a large-diameter portion and a small-diameter portion, and the closure member is inserted into the large-diameter portion of the hollow cylindrical member, an annular surface which connects the large-diameter and small-diameter portions functions as the shoulder surface, and cooperates with an inner circumferential surface of the large-diameter portion to define the female corner portion. In this case, the male corner portion is defined by an end face of the closure member which is to be held in abutting contact with the shoulder surface of the cylindrical member, and an outer circumferential surface of the closure member adjacent to the end face.
The hollow cylindrical member and the closure member are fixed to each other generally by welding, bonding, friction compression, caulking, etc., with the male corner portion being held in abutting contact with the shoulder surface of the female corner portion. The female corner portion, however, is usually rounded to provide a fillet at a boundary between the shoulder surface and the circumferential surface, for easier manufacture of the hollow cylindrical member or the closure member by casting, forging, or cutting, so that the fillet of the female corner portion interferes with the edge of the male corner portion upon engagement of the hollow cylindrical member and the closure member with each other. In this case, there is formed a gap between the shoulder surface of the female corner portion and the abutting surface of the male corner portion, which must be held in abutting contact with the shoulder surface. Since this gap is negligibly small in general, the fixing of the two members is conventionally effected without taking the gap into account. It has turned out, however, that the gap undesirably gives adverse influences on the performance of the piston.
Described in detail, when the hollow cylindrical member and the closure member are fixed to each other by beam-welding the shoulder surface of the female corner portion and the abutting surface of the male corner portion (i.e., the welding surfaces at which the two members are welded together), materials of welded portions of the two members are excessively fused to fill up the gap. In this case, the welded portions of the two members may be recessed due to the excessive fusion of the materials of the two members. In an extreme case, there may be formed a hole in the welded surfaces of the two members, undesirably lowering the weld strength of the two members at the welding surfaces. When the hollow cylindrical member and the closure member are fixed to each other by bonding with an adhesive agent, the thickness of the layer of the adhesive agent formed between the shoulder surface and the abutting surface tends to be larger than a predetermined nominal or optimum thickness value, resulting in reduction of the bonding strength of the two members at the bonding surfaces. When the hollow cylindrical member and the closure member are fixed to each other by pressure welding, the edge of the male corner portion is forced against the fillet of the female corner portion, and collapses so as to substantially follow the fillet, so that the gap between the shoulder surface and the abutting surface is less likely to give adverse influences on the strength of fixing of the two members. Where the fillet of the female corner portion is relatively large, however, the two members may not be fixed together with a sufficient strength. Where the two members are fixed to each other by caulking, the edge of the male corner portion is repeatedly pressed onto the fillet of the female corner portion during operation of the piston, undesirably causing plastic deformation of the edge and the fillet. In this case, the hollow cylindrical member and the closure member which are caulked together may suffer from a rattling movement relative to each other, rendering the piston inoperable.
It is an object of the present invention to provide a method of producing a hollow piston used for a compressor, which has a sufficiently high degree of durability.
The object indicated above may be achieved according to any one of the following forms or modes of the present invention, each of which is numbered like the appended claims and depend from the other form or forms, where appropriate, to indicate and clarify possible combinations of technical features of the present invention, for easier understanding of the invention. It is to be understood that the present invention is not limited to the technical features and their combinations described below. It is also to be understood that any technical feature described below in combination with other technical features may be a subject matter of the present invention, independently of those other technical features.
(1) A method of producing a hollow piston for a compressor including a head portion which is slidably fitted in a cylinder bore of the compressor, and an engaging portion which engages a reciprocating drive device of the compressor which reciprocates the piston, at least the head portion of the piston being hollow, the method comprising the steps of: forming a hollow cylindrical body member which has an open end at at least one of opposite ends thereof, and a closure member which closes the open end of the cylindrical body member, one of the cylindrical body member and the closure member having an annular shoulder surface and a circumferential surface which is adjacent to the annular shoulder surface, the annular shoulder surface and the circumferential surface cooperating with each other to define a female corner portion, the other of the cylindrical body member and the closure member having a male corner portion which corresponds to the female corner portion; and fixing the cylindrical body member and the closure member to each other, so that the male corner portion engages the female corner portion, and wherein the step of forming the cylindrical body member and the closure member comprises at least one of (a) a step of forming an annular groove at a position of one of the annular shoulder surface and the circumferential surface of the female corner portion, the position being adjacent to the other of the annular shoulder surface and the circumferential surface, and (b) a step of forming an edge-free part in the male corner portion.
The piston produced according to the method according to the above mode (1) of this invention has the annular groove which is formed at a position of one of the shoulder surface and the circumferential surface which cooperate to define the female corner portion, the position being adjacent to the other of the shoulder surface and the circumferential surface, and/or the edge-free part such as a chamfer or a round which is formed in the male corner portion. Even if a fillet is present at the boundary between the shoulder surface and the circumferential surface of the female corner portion, it is possible to prevent a conventionally experienced interference between the fillet of the female corner portion and the edge of the male corner portion, by providing the male corner portion with an edge-free part according to the present invention. Accordingly, the piston produced according to the present method is free from the gap conventionally formed between the shoulder surface of the female corner portion and the abutting surface of the male corner portion to be held in abutting contact with the shoulder surface. Therefore, the piston produced by the method of the present invention does not suffer from adverse influences of the above-indicated gap, such as the recess or hole formed in the welded portions due to the excessive fusion of the material, the excessively thick adhesive layer, the insufficient friction compression, and the lowered stability of the caulking portion which results from the caulking of the cylindrical body member and the closure member such that the fillet of the female corner portion and the edge of the male corner portion interfere with each other. Thus, the piston produced according to the present method assures excellent durability while avoiding reduction of the strength of bonding of the closure member to the cylindrical member. The formation of the edge-free part in the male corner portion inevitably reduces an area of contact of the abutting surface of the male corner portion with the shoulder surface of the female corner portion. Accordingly, the cylindrical body member and the closure member are bonded to each other with a higher degree of bonding strength therebetween in an arrangement wherein the annular groove is formed in the female corner portion than in an arrangement wherein the edge-free part is formed in the male corner portion, especially where the closure member is fixed to the cylindrical body member by welding together the shoulder surface of the female corner portion and the abutting surface of the male corner portion, which is to be held in abutting contact with the shoulder surface.
(2) A method according to the above mode (1), wherein the circumferential surface partially defining the female corner portion is an inner circumferential surface.
In the piston produced according to the above mode (2), the hollow cylindrical body member includes, at its open end which is to be closed by the closure member, a large-diameter portion, a small-diameter portion, and a shoulder surface formed therebetween. In this piston, the hollow cylindrical body member has the female corner portion which is defined by the inner circumferential surface of the large-diameter portion and the shoulder surface. Where the closure member is a cylindrical member having an open end and a closed end, the closure member may be fixed to a hollow cylindrical body member having a radially inner annular fitting portion formed at an open end thereof, such that the fitting portion of the hollow cylindrical body member is fitted in a cylindrical portion of the closure member. In this case, the closure member has the female corner portion which is partially defined by an inner circumferential surface of the cylindrical portion.
(3) A method according to the above mode (1), wherein the circumferential surface partially defining the female corner portion is an outer circumferential surface.
In the piston produced according to the above mode (3), the closure member includes a radially inner annular fitting portion which is to be fitted in the open end portion of the hollow cylindrical body member. Where the closure member is a cylindrical member having an open end and a closed end, the closure member may be fixed to a hollow cylindrical body member having a radially inner annular fitting portion which is formed at its open end and which has an outside diameter smaller than that of the other portion, so that a shoulder surface is defined between the annular fitting portion and the other portion. In this case, the hollow cylindrical body member has the female corner portion which is defined by the shoulder surface and the outer circumferential surface of the annular fitting portion.
(4) A method according to any one of the above modes (1)-(3), wherein the hollow cylindrical body member includes a bottom portion and a hollow head portion, the engaging portion being formed integrally with the bottom portion of the hollow cylindrical body member.
In the piston produced according to the above mode (4), the closure member can be constituted by a simple circular plate member. Accordingly, the piston receives a reduced force at a point of fixing or bonding of the closure member and the hollow cylindrical body member to each other, whereby the piston having excellent durability can be easily formed, or the present arrangement permits reduction in a distance of engagement between the closure member and the hollow cylindrical body member, so that the weight of the piston can be reduced.
(5) A method according to the above mode (4), wherein the closure member is a generally circular plate member.
(6) A method according to the above mode (4), wherein the closure member includes a circular bottom plate portion and a cylindrical portion, the closure member, which is fixed to the cylindrical body member functioning as a first cylindrical portion of the piston, functioning as a second cylindrical portion of the piston, the first cylindrical portion and the second cylindrical portion being fixed together at their distal ends.
(7) A method according to any one of the above modes (1)-(3), wherein the cylindrical body member includes a bottom portion and a hollow head portion, while the closure member includes a generally circular closure portion and the engaging portion which is formed integrally with the circular closure portion.
The present arrangement permits easy forming of the hollow cylindrical body member and the closure member by forging.
(8) A method according to any one of the above modes (1)-(7), wherein the step of fixing the cylindrical body member and the closure member to each other comprises a step of beam-welding at least one of the annular shoulder surface and the circumferential surface of the female corner portion, to a surface of the male corner portion, which surface corresponds to the at least one of the annular shoulder surface and the circumferential surface.
(9) A method according to any one of the above modes (1)-(7), wherein the step of fixing the cylindrical body member and the closure member to each other comprises a step of bonding, by using an adhesive agent, at least one of the annular shoulder surface and the circumferential surface of the female corner portion to a surface of the male corner portion, which surface corresponds to the at least one of the annular shoulder surface and the circumferential surface.
(10) A method according to any one of the above modes (1)-(7) and (9), wherein the circumferential surface partially defining the female corner portion is an inner circumferential surface, and wherein the step of fixing the cylindrical body member and the closure member to each other comprises a step of caulking radially inwardly a cylindrical wall which has the inner circumferential surface of the female corner portion.
(11) A method of producing a hollow piston for a compressor including a head portion which is slidably fitted in a cylinder bore of the compressor, and an engaging portion which engages a reciprocating drive device of the compressor which reciprocates the piston, at least the head portion of the piston being hollow, the method comprising the steps of: forming a cylindrical body member which has an open end at at least one of opposite ends thereof, and a closure member which has an annular abutting surface that is to be held in abutting contact with an end face of the cylindrical body member on the side of the open end thereof, and an annular protruding fitting portion which axially protrudes from the annular abutting surface and which is inserted into the open end of the cylindrical body member; and fixing the closure member to the cylindrical body member such that the annular protruding fitting portion of the closure member being inserted into the open end of the cylindrical member, and such that the annular abutting surface of the closure member is held in abutting contact with the end face of the cylindrical body member, and wherein the step of forming the cylindrical body member and the closure member comprises at least one of (a) a step of forming an edge-free part at a radially inner end of the end face of the cylindrical body member, and (b) a step of forming an annular groove at a position of one of an outer circumferential surface and the annular abutting surface of the closure member, the position being adjacent to the other of the outer circumferential surface and the annular abutting surface.
(12) A method of producing a hollow piston for a compressor including a head portion which is slidably fitted in a cylinder bore of the compressor, and an engaging portion which engages a reciprocating drive device of the compressor which reciprocates the piston, at least the head portion of the piston being hollow, the method comprising the steps of: forming a cylindrical body member which has an open end at at least one of opposite ends thereof and which includes a large-diameter portion on the side of the open end, a small-diameter portion remote from the open end, and a shoulder surface between the large-diameter and small-diameter portions, and a closure member which has an annular abutting surface that is to be held in abutting contact with the shoulder surface; and fixing the closure member to the cylindrical body member such that the closure member is inserted into the large-diameter portion of the cylindrical body member with the annular abutting surface of the closure member being held in abutting contact with the shoulder surface of the cylindrical body member, and wherein the step of forming the cylindrical body member and the closure member comprises at least one of (a) a step of forming an annular groove at a position of one of an inner circumferential surface and the shoulder surface, the position being adjacent to the other of the inner circumferential surface and the shoulder surface, and (b) a step of forming an edge-free part at a radially outer end of the annular abutting surface of the closure member.